I think the title explains it pretty well. Attempts to instantiate a ButtplugBrowserWebsocketClientConnector fail, because WebSocket is not imported from ws (despite ws being a dependency).
The workaround I've found is to import websocket in my main script, then define it globally:
import { WebSocket } from 'ws';
Object.assign(global, { WebSocket: WebSocket });
Which works, but isn't ideal.